Vibration damping materials are used to prevent vibration and noise of various structures to insure sustained quietude and have been widely used beneath cabin floors of road vehicles and also applied to rolling stock, ships, aircraft, electric machines, buildings, and construction machines, among other uses. Molded products such as plate products and sheet products produced by using materials having vibration absorbing performance and sound absorbing performance have been conventionally used as raw materials used for such vibration damping materials. However, it is difficult for such molded products to be used at vibration or noise-generation positions having complicated shapes. Therefore, various methods for improving the workability and thereby sufficiently exhibiting the vibration damping property have been investigated. That is, an inorganic powder-containing asphalt sheet has been installed under automotive cabin flooring, for instance, but since the sheet must be secured in position by thermal fusion, improvements in workability and the like are needed and studies are underway on various compositions for vibration damping materials and polymers for the formation of vibration damping materials, for example.
Coating type vibration damping materials (coating materials) have been developed as an alternative material for such molded products. For example, the following vibration damping coating materials have been variously proposed: vibration damping coating materials are sprayed onto positions to be subjected to damping treatment with a spray or applied thereto by any methods, and thus-formed coating film can provide vibration absorbing effect. Specifically, not only aqueous vibration damping coating materials in which synthetic resin powders are blended with vehicles such as asphalt, rubber, and synthetic resin and thereby the hardness of the obtained coating film is improved, but also as materials suitably used for interior parts of cars, vibration coating materials in which activated carbon as a filler is dispersed into a resin emulsion, have been developed. However, even these conventional products do not provide sufficiently satisfactory vibration damping performances. Techniques for further sufficiently exhibiting the vibration damping performances have been desired.
With respect to conventional coating type vibration damping materials, disclosed is an aqueous vibration damping composition prepared by adding a compatibilizing agent to a mixture of aqueous dispersions of two or more kinds of polymers having different glass transition temperatures at a specific ratio (for example, referring to Japanese Kokai Publication No. 2001-152028 (page 2)). In this composition, the mixture of aqueous dispersions of incompatible polymers is used, and the compatibilizing agent is added to cover the incompatibility, and thereby the temperature peak of the vibration damping property can be broad. However, in such a composition, the compatibilizing agent may remain in the vibration damping coating film. Therefore, such a composition has room for improvement in order to sufficiently exhibit the vibration damping performances.
With respect to an emulsion for vibration damping materials containing particles having a core part formed from an acrylic copolymer and a shell part formed from an acrylic copolymer, disclosed is a technique for adjusting glass transition temperatures of these acrylic copolymers (for example, referring to Japanese Kokai Publication No. 2005-105133 (page 2)). Such an emulsion for vibration damping materials shows excellent vibration damping property in a wide temperature range. Therefore, such a technique is industrially very useful. However, such a technique has room for improvement in order that such an emulsion exhibits more excellent vibration damping performances and thereby is more preferably used as vibration damping materials of various structures.